Truss type joist



Dec. 11, 1934. w. B. MILLER ET AL TRUSS TYPE JOI ST Filed Nov. 19, 1931W B MILLER. FELAHK E205KY clam/m4.

Patented Dec. 11, 1934 UNITED STATES TRUSS TYPE J OIST William B.Miller, Lakewood, and Frank Eroskey,

Lyndhurst, Ohio Application November 19, 1931, Serial No. 575,998

4 Claims.

Our invention pertains to a truss-type joist and to the method of makingit.

The object of our invention has been to originate what we are convincedis demonstrably an all-purpose or ideal joist construction, comprising aminimum of weight with a maximum of strength for any specificload-carrying duty and which will be more reliable while moreeconomically manufactured. Specifically, our invention will guaranteeavoidance of an occurrence of secondary stresses either in the top andbottom chords or in the connecting web. The avoidance of bending orother secondary stresses in the web components is achieved in part bythe proper location of the points of intersection of the center lines ofgravity of the web components in the neutral axes of the chords and inpart achieved by inserting the bends of the continuous waveshaped web inarcuate grooves in the stems of the chords so that the curved bendsections are in their entirety braced within the grooves preparatory towelding or otherwise securing them therein; in part by maintenance ofthe constant depth of the web for a given depth of joistregardless ofthe area of the chord members so that the distance between theintersection of the top and bottom chords with the web is a constant;and in part by reason of our unique cross-sectional shape of chordmember with its contrived lateral displacement of metal, with itscontinuous groove in the chord head or flange on the side opposite tothe side from which the stem of the chord projects in order toaccomplish a displacement of metal in required amount and direction andwith its inclosure of the web bends to form a greater area and hencebetter pressure welded job.

It is to be realized that the scope of our invention comprehends manyequivalent methods and constructions; The showing of the drawing and theparticular description are merely specific exemplifications of aplurality of mechanical embodiments and arrangements and performances.

Adverting to the drawing:

Figure 1 is a side elevation of joist embodying the principles of ourinvention. 7

Figure 2 is an enlarged vertical section on line 2,-2 of Figure 1.

Figure 3 is a still further enlarged fragmentary elevational detail ofthe interlocked connection between web bends and chord members withcertain important dimensions measured and designated. I g i I Figure 4is a section on line 4-4 of Figure 3, likewise with certainmeasurements.

1 complete joist,

Figure 5 is a view showing one of the arcuate grooves in the chordmembers.

Figures 6 to 9 inclusive portray four sectional views of modified chordmembers embodying featured principles of our invention.

Our fabricated metaltruss-type of joist comprises a top chord member 1and bottom chord member 2 and. a connecting web structure 3 ofcontinuous zigzag or wave-like shape. While the cross sectional shape ofthe upper and lower chord members 1 and 2 to comprise a stem and aflange is the same, most essentially at so-called panel points where thebends of the web are secured thereto, it will be observed that the lowerchord member 2 has its ends bent upwardly and its extremities closer tothe extremities of the upper chord member for the interposition at eachend of separated fillers 4 and 5 between each pair of which is a hole 6for the purpose of facilitating any appropriate anchoring means. Themethod of securement of the two ends of the chord members is of noconsequence to our invention. The neutral axis of the upper chord memberhas been designated with the numeral '7, the center of gravity lines ofthe angle-forming parts of the web have been designated (in Fig. 3) withthe numeral 8 and the neutral axis of the lower chord member with thenumeral 9.

Inviting attention to Figures 3 and 4 where certain dimensionalmeasurements which are of importance to our invention are graphicallydisplayed, we state the numeral 10 to designate the thickness of thechord flange, the numeral 11 to designate the distance between the lowersurface of the chord flange and the bottom of the stem S of the chordmember, which latter approximates a T shaped cross section, the numeral12 to designate the distance between the neutral axis 7 of the chordmember 1 andthe bottom of the T, the numeral 13 to designate thedistance between the neutral axis 7 and the top of the chord member orthe top of its head or flange, the numeral 14 to designate the distancebetween the bottom of the stem S and the bottom of a continuous uppergroove to be later explained, the numeral 15 to designate the verticaldistance between the bottom of the continuous upper groove and the topof the chord member, the numeral 16 to designate the distance betweenthe top and bottom of the the numeral 17 to designate the distancebetween the bottoms of the upper and lower; grooves (to be laterexplained) at panel points, the numeral 18 to designate the distance ofrecession of the bendsBa of the web 3 into the stem S of each chordmember, the numeral 19 to designate the radius of curvature of the bends3a, the numerals to designate the constant angles of each diagonal webcomponent with a vertical line, the numeral 21 to designate the width ofthe chord flange, the numeral 22 to designate the outer and constantwidth of the upper and continuous groove, the numeral 23 to designatethe variable width of the lower end of the stem S, the numerals 24 and25 (Figure 2) to designate the welding burrs, and the numeral 26 todesignate a continuous longitudinally extending groove along the centerline of the flange of the chord member, which groove 26 on the side ofthe chord member opposite to the location of the stem is to displacemetal in such an amount and direction as to insure final intersection ateach panel point of all center of gravity lines.

The external vertical dimension of each chord member is according to ourinvention to remain constant for all sizes or for all areas. Always, thevertical distances between the neutral axis 7 and both the top andbottom of the complete joist is to remain constant. Preferably, thedistances of 15 and 22 as dimensions of the continuous groove areconstant for any area of chord section for the purpose of standardizingthe top rolling performance and facilitating joist assembly. A series ofchord members will have their dimensions 12, 13, 14, 15 and 16 constantand their dimensions 10, 11 and 21 variable to comply with therequirement for different areas having different load carrying capacity.The angle 20 which each component or section makes with a chord is aconstant for all depth of joists and all sizes of webbing andcorrespondingly dimensioned series of chord members. The depth of joistis determined by its span. The variable area (width times thickness of asection) is determined by the expectable load.

It is to be understood that the arcuate grooves 27 in the extremities ofthe stem S are aligned and longitudinally spaced but, as exemplified,

those in the upper chord member are staggered with relation to those inthe appositioned stem of lower chord member so that the bends 30; may bealmost entirely accommodated to be eifectively braced therein. In sointerlocking the bends 3a in the stems of the chord members preparatoryto final pressure welding, a compensation is provided for any apparentloss of area due to the accommodating displacement of metal by reason ofthe existence of the outer groove 26, by the insertion of the web bendswhich become an integral part thereof, to achieve the neutral axis andcenter lines of gravity intersections earlier mentioned as in conformitywith sound engineering in order to avoid incalculable secondarystresses. It is mentioned that in all joists of a given depth the out toout dimension of the web bends is a constant regardless of thecombinations of sectional areas (thickness of the chord stem and flangeand width of the latter) of chord members and webs. Moreover, thespacing of the arcuate grooves 27 for any chosen depth of joist willremain a constant, regardless of the adopted size combination of chordmember and web, in order to bring the gravity line intersection pointswhere desired and incidentally to standardize manufacture.

Secondary stresses are not set up because of the perfect intersection ofthe web angles with the chord members and because the stresses becometransmitted directly along oblique web sections which are whollystraight between points of contact at their ends. No secondary stressesare set up in the chord members because of the correct intersection ofthe center lines of gravity. By setting the bends of the web into thearcuate grooves or of other conforming contour the bends of the web arefirmly braced throughout their entire curved extent and offer a largerarea for more secure welding. The constant depth of the web maintainedfor a given depth of joist regardless of the area of the chord membersso that the distance between the top and bottom chord members and web isa constant, makes possible, together with insertion of the web bends,realization of a straight line between points of contact of the webcomponents with the chord members and makes it possible to employ websof less or smaller section than required to be used in joists where theweb components are not so braced at their points of connection with thechord members. By having thus increased the area of the weldedconnections a joist is obtained which is not only better able to resistthe loads that it will have ultimately to carry, but stronger forresisting the construction stresses that are set up due to constructionloads, transportation or any other handling. During the weldingoperation the desired accurate fit over the full contour of the groovesinto which the web bends are inserted is readily accomplished by theapplication of adequate pressure. The continuous groove 26 serves aptu'pose of decreasing the thickness of the metal between the weldingelectrodes to facilitate and cheapen and also preestablishes the neutralaxis of the chord member and its'shape is maintained by thetemporaryoccupancy thereof of one of the welding electrodes and to allowthe web bends to be pressed and secured into the staggered inner chordgrooves while maintaining the important intersection (Z, Figure 3) ofthe center lines of gravity with neutral axes at all panel points.

It is to be understood that while the joist illustrated in Figure 1 hasonly nine panels the number will vary according to the span and depth ofthe joist, mindful that the zig-zag angles are always maintaineduniform, because of the desideratum of gravity line intersection. Thegroove and web bend interlock favors correct manufacture by maintainingthe alignment of the web and resisting a tendency of the chords or websto become distorted or to move out of place.

It is desirable to be able to change the size of the web members toaccommodate varying loads without disturbing in any way the intersectionof the gravity lines. This is accomplished by adjusting the location ofthe radial point 190. while the angle of inclination of the line 8remains unchanged.

As one example of the method in which our joist may be assembled we citeas follows:

Starting with straight chord and web members of the required section,the chord members of required section'are first out to the proper lengthfor the particular length of joist to be manufactured allowingadditional length of material for the lower chord to take care of bentup ends.

The chords are then grooved at the proper intervals to receive the bendsof the zigzag web member. The ends of the lower chord member are thenbent up so as to form a connection with the upper chord member whenassembled. The web members are then bent into zig-zag shape so that theinterval of the bends conforms to the grooves in the chord members. Nextthe web is fitted to the chords while both are on a table so that eachbend in the zigzag web is recessed properly into its respective groove.

The elements of the joist are then clamped into position at intervalsand the joist is then run through a welding machine preferably of thepressure welding type. The type of welding machine would preferably beone having one electric element of such shape as would conform to thecontinuous grooved profile of the joist section and the other of suchshape as would conform to the shape of the bends of the zigzag websection.

During the assembly and welding process of the joist, machine guides ofthe electric welding machine will fit into the continuous groove of thejoist chords and hold the joist in alignment as it advances through thewelding machine, making a finished product of precision. At the sametime that the guides in the continuous grooves of the chord members areholding chord alignment the accurate grooves of the chord members holdthe web in alignment and prevent creeping of the joist elements.

After all the web member welds are made the end chord connections arewelded to complete the joist fabrication.

Figures 6 to 9 are all modifications of the cross sectional design ofthe chord members and since they so slightly differ they will be givenlike reference characters to designate like parts. Each comprises aflange 28 provided along its median line with a continuous metaldisplacing compound groove 29, each includes a stem 30 and while theforms shown in Figures 6, '7 and 9 additionally show stem grooves 31,Figure 8 differs in showing one defining wall of its groove 31 inelevation.

We consider one important feature of novelty of our invention to residein any one point of connection of one chord member with the web wherebywe have established. the possibility and realized the great advantage ofemploying variable chord sections and variable web sections with thelatter having components converging at panel points while constantlymaintaining for every size, strength and weight of joist an intersectionat one unvaryingly positioned point Z, (Figure 3) at each panelconnection between the gravity center lines of said web components andthe horizontal and vertical neutral axes of the chord section.Consonantly, we can successfully employ in a trusstype metal joist achord member of varying sectional area as well as two chord members ofcomparatively different sectional areas while always maintaining theirhorizontally extending neutral axes in intersection with their verticalgravity center line at one unvaryingly positioned point. Any type ofcontinuous zig-zag web having its diagonal sections forming the sameangle with the vertical while the web has a uniform vertical dimension,may be secured to a pair of chord members so that the completed joisthas a uniform external vertical dimension even though the areas of thetop and bottom chord members vary and yet always maintain theintersection at panel points of all center lines of gravity passingtherethrough.

We claim:-

1. A metallic joist comprising top and bottom chord members fashionedwith spaced arcuate grooves in staggered apposition and a web structurehaving bend portions and reversely inclined diagonal portions extendingbetween and secured in said arcuate grooves of said top and bottom chordmembers, the entire depth dimensions of said chord members beingconstant irrespective of limited variations in thickness of theassembled parts yet remaining so arranged that the respective center ofgravity lines constantly intersect at points substantially lying in theneutral axes of said chord members, said groove-interlocking connectionsbeing adapted to resist secondary stresses in the web structure and alsoc-ompensatorily to replace the metal displaced from said grooves.

2. A metallic joist comprising top and bottom chord members fashionedontheir outer sides with a longitudinally extending groove and a zig-zagweb structure having portions secured to said top and bottom chordmembers, the entire depth dimensions of said chord members beingconstant and the distances between the bottom of each groove and the topand bottom of its chord member being constant irrespective of limitedvariations in thickness of the assembled parts yet remaining so arrangedthat the respective center of gravity lines of angle-forming parts ofthe web structure constantly intersect at points substantially lying inthe neutral axes of said chord members.

3. In a truss-type joist, the combination of a pair of parallelly spacedchord members of inversely arranged T-shaped cross section each tocomprise a stem and flange, said appositioned stem ends each beingfashioned with a row of grooves, the grooves of one row being staggeredwith reference to the grooves of the other row, said flanges each beingfashioned opposite its stem with a longitudinally extending groove, awaveshaped web having staggered bends occupying said stem grooves inboth chord members to establish intersection of pairs of convergingcomponents of said web substantially in the neutral axes of said chordmembers and means for securing said bends in said grooves.

4. A metal truss-type joist comprising a continuous wave-shaped web anda pair of chords of T shaped cross section and with their stemsappositioned and fashioned with relatively staggered grooves for thereception of the crests of said web, the intersection of said web insaid chords being so contrived that the center of gravity lines of partsof said web intersect at points in the neutral axes of said chords.

WILLIAM B. MILLER. FRANK EROSKEY.

